1. Field of the Invention
This invention relates broadly to method and apparatus for the transfer molding of thermosetting polymeric materials. More specifically, this invention relates to method and apparatus for reducing or substantially eliminating the amount of relatively expensive thermoset polymeric material customarily remaining as cull and runners in transfer molding apparatus at the conclusion of a molding cycle.
2. Description of the Prior Art
In the transfer molding of thermosetting polymeric materials as conventionally practiced, a preform of such material, which may have been heated dielectrically previously, is placed in a heated transfer chamber. A ram is advanced into the transfer chamber against the preform and forces the preform material through the runners of the molding apparatus to the several die cavities. At the conclusion of the molding cycle, the apparatus including dies is opened, and the molded articles removed from the die cavities. That preform material remaining as cull and runners outside the die cavities, which material has set, is removed. Due to the irreversibility of the setting of the material, the cull and runners cannot be reused in a subsequent molding operation and must therefore be discarded as scrap or ground and used as filler for other purposes. Since thermosetting polymeric materials are relatively expensive, losses thereof as scrap for the reasons hereinabove noted represent substantial economic charges against the efficiency of the operation.
There is no prior art in the field of transfer molding of thermosetting polymeric materials teaching method or means for reduction or substantial elimination of losses of desirable thermosetting polymeric materials remaining as runners and cull at the conclusion of a molding cycle.
Prior art of general interest in the broad field of molding polymeric materials is found in the following U.S. Patents:
U.s. pat. No. 2,269,953 (1942) to Morin et al. PA1 U.s. pat. No. 3,650,654 (1972) to Schwartz PA1 U.s. pat. No. 3,599,290 (1971) to Garner PA1 U.s. pat. No. 3,221,373 (1965) to Kwan PA1 U.s. pat. No. 2,627,087 (1953) to Hendry PA1 U.s. pat. No. 2,327,079 (1943) to Wacker
The Morin et al. patent above noted bears at most a superficial resemblance to one aspect of the present invention in that several charges of polymeric material are arranged in a cylinder and the charges are injected seriatim under pressure into a die cavity. However, the Morin et al. patent is directed only to the molding of thermoplastic polymeric materials, the charges are of the same thermoplastic polymeric material although the charges may be colored differently apparently to produce a variegated product, and all of the charges are injected into the die cavity leaving nothing in the passageway leading to the die cavity.